Laser passivation of metal surfaces

ABSTRACT

A method of using laser energy for treating a metal work-piece to modify chemical properties of a surface of the metal work-piece. The method includes the step of applying a material to a surface of a metal work-piece. The material is corrosive with respect to the surface. The method also includes the step of improving a resistance to corrosion of the surface by initiating a chemical reaction between the corrosive material and the surface with a laser.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to treatment of metal surfaces with a laser.

2. Description of Related Art

Lasers can rapidly heat a surface of a work-piece for adjusting properties of the surface. An absorptive coating can be applied to the surface to be heated to enhance the energy transfer from the laser to the work-piece. By using a laser to quickly heat a surface, conventional quenching by a gas or a liquid is unnecessary since only the shallow surface layer is heated. The part will actually self-quench, due to the extremely high heat differential between the surface layer heated by the laser and the remainder of the work-piece. In another process, such as carburizing or induction heating, a part may be heated in one operation, and, if necessary, be rapidly quenched by a gas or a liquid. Laser radiation can be generated by CO2, Excimer or Nd-YAG lasers, diode lasers; some of these lasers can achieve intensities of more than 10⁶ watt/cm2.

SUMMARY OF THE INVENTION

A method of using laser energy for treating a metal work-piece to modify chemical properties of a surface of the metal work-piece. The method includes the step of applying a material to a surface of a metal work-piece. The material is corrosive with respect to the surface. The method also includes the step of improving a resistance to corrosion of the surface by initiating a chemical reaction between the corrosive material and the surface with a laser.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present invention will become more readily appreciated when considered in connection with the following detailed description and appended drawings, wherein:

FIG. 1 is a simplified flow diagram illustrating a first exemplary method for practicing the invention;

FIG. 2 is a schematic diagram illustrating the first exemplary method being practiced;

FIG. 3 is a simplified flow diagram illustrating a second exemplary method for practicing the invention;

FIG. 4 is a schematic diagram illustrating the second exemplary method being practiced;

FIG. 5 is a simplified flow diagram illustrating a third exemplary method for practicing the invention; and

FIG. 6 is a schematic diagram illustrating the third exemplary method being practiced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A plurality of different embodiments of the invention are shown in the Figures of the application. Similar features are shown in the various embodiments of the invention. Similar features have been numbered with a common reference numeral and have been differentiated by an alphabetic designation. Also, to enhance consistency, features in any particular drawing share the same alphabetic designation even if the feature is shown in less than all embodiments. Similar features are structured similarly, operate similarly, and/or have the same function unless otherwise indicated by the drawings or this specification. Furthermore, particular features of one embodiment can replace corresponding features in another embodiment unless otherwise indicated by the drawings or this specification.

A first exemplary process according to the invention is shown in FIGS. 1 and 2. The process starts at step 10. At step 12, a material 14 is applied to a surface 16 of a metal work-piece 18. The material 14 is corrosive with respect to the surface 16 and, as a result, the metal work-piece 18. In the exemplary embodiment of the invention, the metal work-piece 18 is ferrous and the material is at least one of sodium nitrate (NaNO3), sodium nitrite (NaNO2), potassium nitrate (KNO3), and potassium nitrite (KNO2).

In the first exemplary embodiment of the invention, the material 14 can be mixed with water to form a solution and sprayed on the surface 16. The material 14 is substantially non-hazardous; as a result, the inventive method is less costly than other, known methods for treating metal work-pieces to reduce the likelihood of corrosion. The materials set forth above are not completely non-hazardous. The materials are not inert. However, the materials are substantially less toxic than materials used in chrome plating; a process that the present invention can replace. The solution can also include a surfactant to promote wetting of the surface 16 by the solution. The solution is then dried before the laser treatment. The height of the dried solution is exaggerated in FIG. 2.

The process continues to step 20 where a laser 22 directs a beam 24 of energy at the surface 16. The exemplary laser 22 is a 4 KW diode laser with a rectangular beam of 0.5 mm by 12 mm. The energy of the beam 24 initiates a chemical reaction between the corrosive material 14 and the surface 16. The exemplary beam 24 is passed along the surface 16 at about 3 meters/minute, where the short axis of the beam is parallel to the treatment path. The chemical reaction results in a chemically converted layer at the surface 16 integral with the metal work-piece 18. The surface 16 has improved corrosion resistance after chemical reaction between the material 14 and the surface 16. The process ends at step 26.

A second embodiment of the invention is shown in FIGS. 3 and 4. In the second exemplary embodiment of the invention, the process starts at step 10 a. At step 12 a, a material 14 a is applied to a surface 16 a of a metal work-piece 18 a. At step 20 a, a laser 22 a directs a beam 24 b of energy at the surface 16 a to initiate a chemical reaction and improve a corrosion resistance of the surface 16 a. The steps 12 a and 20 a are performed concurrently. A solution of material 14 a and water can be sprayed directly into the laser 22 a and surface 16 a interaction zone with a nozzle 28 a. Performing the steps 12 a and 20 a concurrently can eliminate the need to dry the solution. The process ends at step 26 a.

A third embodiment of the invention is shown in FIGS. 5 and 6. In the third exemplary embodiment of the invention, the process starts at step 10 b. At step 12 b, a material 14 b is applied to a surface 16 b of a metal work-piece 18 b. The step 12 b is carried out by immersing or submerging the surface 16 b in solution of the material 14 b in water. At step 20 b, a laser 20 b directs a beam 24 b of energy at the surface 16 b to initiate a chemical reaction and improve a corrosion resistance of the surface 16 b. The beam 24 b penetrates the surface 30 b of the solution to reach the surface 16 b of the work-piece 18 b. The process ends at step 26 b.

The exemplary embodiments of the invention provide numerous advantages in the field of brake rotors and pistons. The chemically-altered surface 16 will not delaminate or peel off the metal work-piece 18. In addition, the process uses simple salts and not hazardous materials, such as heavy metals. Furthermore, the process is relatively quick, unlike immersion in salt baths, for example, that may take thirty minutes. The exemplary embodiments could be performed on the production line. The invention, being broader than the exemplary embodiments, may not provide these exact advantages in other fields and may provide other advantages.

Many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. 

1. A method of using laser energy for treating a metal work-piece to modify chemical properties of a surface of the metal work-piece comprising the steps of: applying a material to a surface of a metal work-piece wherein the material is corrosive with respect to the surface; and improving a resistance to corrosion of the surface by initiating a chemical reaction between the corrosive material and the surface with a laser.
 2. The method of claim 1 wherein said applying step is further defined as: spraying a solution of water and at least one of sodium nitrate, sodium nitrite, potassium nitrate, and potassium nitrite on the surface; and drying said solution prior to said improving step.
 3. The method of claim 1 wherein said applying step is further defined as: submerging the surface in a solution of water and at least one of sodium nitrate, sodium nitrite, potassium nitrate, and potassium nitrite.
 4. The method of claim 1 further comprising the step of: combining a surfactant with the material prior to said applying step.
 5. The method of claim 1 wherein said improving step includes the step of: directing a diode laser at the surface.
 6. The method of claim 1 wherein said applying step and said improving step are further defined as occurring concurrently.
 7. The method of claim 1 wherein said applying step is further defined as: applying a non-hazardous material to the surface of the metal work-piece wherein the material is corrosive with respect to the surface.
 8. The method of claim 1 wherein said improving step is further defined as: forming a chemically converted layer at the surface integral with the metal work-piece. 